Itchy easily has the funniest lines in this movie, especially since most of it is Dom De Luise ad libbing.
Itchy:(On Ann-Marie) Hey boss—maybe she only talks to rats....
Charlie: Oh, don't be stupid. She talks to me, doesn't she?
Itchy: Yeah, she talks to you: THAT MAKES YOU A RAT! (Busts a gut laughing)
"Try that again, you, and you are glue!"
"I don't care if it's his...his Bar Mitzvah! That horse is a gluepot!"
(after Anne Marie points out which horse will win and Charlie starts off to place the bet) "Oh yeah, sure, with what dough, boss?"
(while looking for the "monster") "Charlie, just know we're both gonna die!"
(after Charlie grabs Itchy's tail) "WHY DONTCHA TELL SOMEBODY YOU"RE GONNA DO THAT?!?"
"And your hands are cold, too!" Although there's some Fridge Horror there: Charlie was just dead for a few minutes.
And when he tries to flee, because he doesn't want to see "the monster", Charlie grabs him by his tail and drags him back, and Itchy freaks out, yelling, "SOMEONE'S GOT ME!"
"So call me a mixed-up pup!" "You're a mixed-up pup!"
Any time Carface tells Killer to shut up.
When Charlie comes back to Earth, he pops out of the water, scaring a cat.
Charlie telling one of the pups to "eat the box" when he asks for more pizza. On paper, it's not that funny, but Burt Reynolds' blasé reading makes it hilarious.
Charlie dances with the Heavenly Whippet (later known as Annabelle) and compliments her on her dancing, saying she has natural rhythm... but watch her feet. She's not actually dancing, Charlie's just swinging her around on his own; the only time her feet touch the cloud they're on, she's just making a vaguely ballet-like toe-point. Of course, Charlie is just trying to distract her.
Charlie carrying Anne-Marie out of her room at Carface's casino, going on a lengthy description of how nice his house is before nonchalantly adding "I live in a cab!"
Charlie begrudgingly tucking Anne Marie into bed in his cab and, later, kissing her goodnight, especially the gargoyle-like face he makes after he gives her cheek the most pathetic, non-affectionate little lick with the tip of his tongue.
Charlie reading Anne-Marie the story of Robin Hood. The book in front of them is War and Peace.
Anne Marie: Was [Maid Marion] pretty?
Charlie: (chuckles) Oh, she was to die for!
(Shows her a graphic illustration of someone being run through with a sword).
Followed by this joke, which anyone who's ever read a child their bedtime story can relate to.
Charlie: But the whole gang wondered, would Maid Marion marry him? And...
All the while, Itchy is complaining that Robin Hood is a chump for not taking his cut of the money he steals for the poor.
The Running Gag of Charlie getting disgusted when Anne Marie kisses him on the nose. At one point, he immediately grabs the towel Itchy was using to clean the bar with to wash his muzzle once she's out of sight.
Similarly, the animation of his reaction to King Gator finding him and saying "Delicious!" before giving chase.
Charlie convincing Itchy he's not dead.
Charlie:[Clamps his whole paw around Itchy's muzzle] Itchy. I'm not a ghost. I'm not dead. Now be quiet. I'm gonna take my hand away from your mouth, and you're gonna be quiet, aren't ya? Itchy: Mm. Mm-hmm. Charlie: Ha ha. That's my pal. [lets go] Itchy: WAAAAAAAAAAAAAHHHH!!! Charlie: Will you shut up?! Itchy, I'm alive! Look, Iook! Do ghosts have fleas?
And before that, Itchy freaking out, thinking that Charlie is a ghost. Only reasonable since he did see him get run over by a car.
Itchy:AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAGH!!!(Tries to dart for it, but Charlie grabs him, trying to shush him) It—CHARLIE! (wriggles out of Charlie's grasp and again tries to flee, but Charlie grabs him and tries to shush him again) Oh NO!—You're a GHOST! (wrestles away from Charlie and jumps out of his room and scrambles into the main area followed by Charlie) Get back! Get back, don't hurt me! (pulls out a toolset) Uh, here, take my nine-piece ratchet set! (flings it at Charlie and climbs up onto a table, pulling out an oilcan) My oilcan! (chucks oilcan at Charlie and then grabs a hood ornament as Charlie climbs up onto the table, glaring at him) And—uh-uh-uh, don't go away—without my Rolls Royce hood ornament—! (hits Charlie on the head with hood ornament)
The epic failure of Charface and his goons trying to shoot Charlie, Killer's ray gun swerving all over the place and firing in all directions except Charlie!
Even the otherwise Tear Jerker ending has a little humor in it when Charlie's ghost asks Anne Marie how she's doing and she cheerfully replies "Okay!"
Earlier, when she cheerfully announces to the Wallet Family that she lives with Charlie in the junkyard.
Following that heartbreaking ending, we get this great bit of Comic Relief as the credits start.